In the case of gasoline engine powered mowers, it has hitherto been usual practice to mount an air-cooled engine therein to provide a motor vehicle which is low in cost, light in weight and compact in size. However, the use of air-cooled engines has given rise to problems of noise and air pollution. In view of this fact, there has in recent years been a tendency to use liquid-cooled engines in this type of apparatus.
In the art of cooling engines with liquids, such as aqueous coolant solutions and water, it has hitherto been usual practice to mount a vertically-oriented radiator in front of a liquid-cooled engine having a crankshaft oriented horizontally and extending lengthwise of the vehicle containing the engine. A cooling fan is generally placed at the rear of the radiator. One example of the liquid-cooled engines of the aforesaid construction is described in Japanese Utility Model Laid-Open No. 19299/83. The art disclosed in this document deals with the structural arrangement of a water-cooled engine mounted in a tow motor having a driver's cab, in which an engine having a crankshaft extending lengthwise of the vehicle is connected to a forward end of the transmission case. A front wheel cover extends forwardly from the engine and supports thereon a radiator which is oriented vertically.
In a motor vehicle equipped with this type of engine, the crankshaft is located in a position which is considerably lower in level than the center of a fan for cooling the radiator. As a result, an idler pulley has to be mounted at a rear portion of the cooling fan supported by the engine and a belt is trained over this pulley and a drive pulley is located at the outer periphery of the crankshaft to drive the fan. In this construction, the belt drive system is inevitably mounted in front of the engine, and auxiliary machinery is also mounted in this position in many applications because of the ease with which maintenance and inspection can be effected. This makes it necessary to mount the radiator in a position remote from the front of the engine. As a result, the engine and radiator occupy more space than is necessary, thereby making it impossible to obtain compact dimension in a motor vehicle equipped with such a liquid-cooled engine. Furthermore, the use of a belt drive system increases the production cost of a motor vehicle equipped with this type of liquid-cooled engine of the aforesaid construction. However, in the motor vehicle of the aforesaid construction, the presence of the belt drive system increases the distance between the engine and radiator and if the radiator were supported by the engine, the radiator would vibrate to such an extent damage might be caused thereto. Alternatively, if the radiator is mounted to the front wheel bracket as proposed in the document referred to hereinabove, then there is the disadvantage that the support structure for the radiator requires a complex construction. Furthermore, if the radiator were supported by the front wheel bracket and the cooling fan by the engine, mutual interference would take place between the radiator and cooling fan because the systems supporting them differ from each other. To avoid this trouble, it would be necessary to increase slightly the tip clearance between the outer periphery of the cooling fan and the fan duct. However, this places limitations on the efficiency with which the cooling fan can operate to perform its function. Additionally, the use of a belt drive system for transmitting drive force from the crankshaft to the cooling fan might cause overheating to occur in the engine due to possible loosening of the belt.
Accordingly, there is a need for an improved liquid-cooled power unit which significantly reduces the amount of space that the engine and radiator occupy and one which is easily installed in a vehicle or enclosure as a unit. A need also exists for a liquid-cooled power unit which eliminates the need for a belt to drive the cooling fan and which additionally reduces engine noise and exhaust pollutants.